Docker Counter replicas in docker conteiners

version: '3.7'
services:

  dev_mysql:
    image: mysql:8.0.16
    command: --default-authentication-plugin=mysql_native_password 
    environment:
      - MYSQL_DATABASE='dev_mysql'
      - MYSQL_USER='user'
      - MYSQL_PASSWORD='password'
      - MYSQL_ROOT_PASSWORD='xxxxxxxxxxxxxxx'
      - REPLICA={{.Task.Slot}}
    ports:
      - 3355:3306
    networks:
      - crm_network
    deploy:
      replicas: 6
      restart_policy:
        condition: any
      update_config:
        parallelism: 1
        delay: 10s
        order: start-first
      resources:
        limits:
          memory: 2048M
          cpus: "2"
networks:
  crm_network:
    external: true